Solar Wind Electron, Proton, and Alpha Monitor
(SWEPAM)

for the Advanced Composition Explorer (ACE)

Los Alamos National Laboratory
Sandia National Laboratory

The purpose of the Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM)
is to provide detailed knowledge of solar wind conditions to aid in the
interpretation of data measured by the ion and the electron composition
monitors of the ACE mission payload. This purpose is achieved by modifying
the spare Ulysses BAM-E and BAM-I instruments to provide high quality
measurements of electron and ion fluxes in the low-energy solar wind range
(electrons: 1 to 1240 eV; ions: 0.26 to 35 keV).

Simultaneous electron and ion measurements are made using two separate
instruments. Each instrument consists of a curved plate, >90° bending angle
electrostatic analyzer (ESA) followed by biased channel electron multipliers
(CEMs) spaced along the exit apertures of the ESAs. Different CEMs sample
different portions of the fan shaped fields of view (FOV), allowing
measurement of particle arrival directions relative to a spacecraft
coordinate system of azimuthal and polar angle. Polar angle from the
sun-pointing spin axis is given by the CEM number, while azimuthal angle
is given by phase of spacecraft spin. Later, this local coordinate system
is converted to a standard solar ecliptic frame of reference for data
analysis.

Each instrument is powered by its own low-voltage converter, sweeping ESA
high-voltage power supply, and fixed level CEM high-voltage supply. Each
instrument is operated with an independent microprocessor based electronics
control and data handling system.

SWEPAM is one of the four instruments that supplies data for the NOAA
Real Time Solar Wind 24-hour monitoring of
Space Weather.

SWEPAM is a joint project of the Space and Atmospheric Sciences Group at
the Los Alamos National Laboratory (LANL) and the
Center for Monitoring Systems
and Technology at the Sandia National Laboratory (SNL).